Currently, human coronaviruses mainly infect the epithelial cells of the respiratory tract. COVID-19 is primarily transmitted from person-to-person through respiratory droplets which are released when someone with COVID-19 sneezes, coughs, or talks. These infectious droplets may then land in the nose or mouth of a person nearby and possibly be inhaled into the lungs. Respiratory droplets can land on hands, objects, or surfaces around the person when they cough or talk. Individuals can then become infected with COVID-19 from touching hands, objects or surfaces containing droplets and then touching their eyes, nose, or mouth.
The risk of transmission of the COVID-19 infection is highest when people are in close proximity for a longer period of time and infectious particles can be inhaled over longer distances, particularly indoors in poorly ventilated and crowded spaces. Although touching a contaminated surface or object can lead to infection, it does not appear that this route contributes substantially to transmission. In addition, individuals who are infected but do not show symptoms can transmit the virus to another person up to two days before symptoms may appear. Moreover, individuals can remain infectious for up to ten days after the onset of symptoms in moderate cases and up to twenty days in severe cases.
